There are two different lines for quantity supplied, and quantity demanded. They are inverse in inclination
At a price of $5 supply and demmand are the same.
So we need to find how many slices of cake canbe sold at $2
Trace the supply demmand curve ,that is represented by
Q supplied + Q demanded = $ 5
At a price of $2 ,then shortage in price would be 8-2 =]$6
and with $6 can be buyed 6/2 =3 slices.
So then final answer is a shortage of 3 slices.